To inspect a defect in a structure or a component, or a peeling state of a void or a joint, an ultrasonic inspection apparatus is used that can visualize such a state. The ultrasonic inspection apparatus uses an ultrasonic transducer constituted by a piezoelectric conversion unit formed into a matrix or linear array shape to scan an object to be inspected and inspect a defect or the like.
The ultrasonic inspection apparatus includes a scanner mechanism that drives the ultrasonic transducer. The scanner mechanism is constituted by a Cartesian robot having an X-axis, a Y-axis, a Z-axis, and a required axis such as an A-axis (rotation axis in an X-axis direction), a B-axis (rotation axis in a Y-axis direction), or a C-axis (rotation axis in a Z-axis direction), or an industrial robot basically including an arm mechanism. The scanner mechanism is driven based on control by a control mechanism or the like, and thus the ultrasonic transducer mounted to the scanner mechanism automatically performs a flaw inspection of a predetermined range on a surface of the object to be inspected.
For the ultrasonic transducer to automatically perform a flaw inspection of a predetermined range, scanning path information of the scanner mechanism needs to be previously generated. The scanning path information is generated based on a surface shape of the object to be inspected, for example, with an opening width of the ultrasonic transducer as one scanning width.
A method of generating scanning path information includes a method of previously generating scanning path information using computer software based on shape design data of an object to be inspected. By this method, scanning path information can be relatively easily prepared. However, the prepared scanning path information is scanning path information based on ideal shape design data, and there is a possibility that a shape of an actual object to be inspected does not match a shape of the object to be inspected on the shape design data due to working accuracy in production of the object to be inspected. Furthermore, in an ultrasonic flaw inspection, the object to be inspected is placed in a predetermined position in the scanner mechanism, but it is difficult to place an object to be inspected having a complicated shape in a predetermined position with high reproducibility.
Another method of generating scanning path information includes a method of driving an ultrasonic transducer with a scanner mechanism on a surface of an object to be inspected, thus teaching and registering each of passage points on an actual scanning path, and generating, as scanning path information, the passage points of the scanner mechanism connected as a scanning path. In this method, the scanner mechanism is driven at each of the passage points on the scanning path to teach and register the scanning path of the scanner mechanism, which requires an enormous amount of time and operation. In particular, if a driving unit provided in the scanner mechanism has a complicated configuration, a very complicated procedure and operation are required.
To perform an ultrasonic flaw inspection with high accuracy, ultrasound transmitted by an ultrasonic transducer needs to be incident on an inspection region of an object to be inspected at a constant angle. For an ultrasonic inspection apparatus that performs a flaw inspection by an aperture synthesis, a constant distance needs to be maintained between an ultrasonic transducer and a surface of an object to be inspected.
Then, an ultrasonic flaw inspection apparatus has been proposed that can hold an object to be inspected and an ultrasonic transducer with a constant distance therebetween, and can cause ultrasound to be incident on the object to be inspected at a constant angle (for example, refer to Japanese Patent Laid-Open Publication No. 63-309852 (Patent Document 1)).
The ultrasonic flaw inspection apparatus disclosed in the above Publication includes a distance sensor at a lower end of a drive shaft substantially perpendicular to a scanning stage of a scanner mechanism, and the distance sensor performs scanning on the object to be inspected. Based on measurement data of the distance between the object to be inspected and the distance sensor obtained by scanning, shape data of the object to be inspected that is coordinate data of the scanner mechanism is calculated and stored in a memory. Further, in scanning, scanning path information with each point of the shape data of the object to be inspected as a passage point is prepared and open loop control of a driving mechanism is performed.
Furthermore, an automatic ultrasonic flaw inspection method has been also proposed of obtaining shape data of an object to be inspected by performing an interpolation using a spline function, and performing position control of an ultrasonic transducer (for example, see Japanese Patent Laid-Open Publication No. 5-45347 (Patent Document 2)).
The automatic ultrasonic flaw inspection method performs an interpolation of obtained distance data using a spline function, thereby reducing time and labor required for preparing shape data.
With the ultrasonic flaw inspection apparatus in Patent Document 1, to obtain the shape data of the object to be inspected, shape data including a passage point on a scanning path on the object to be inspected needs to be previously obtained, which involves an enormous time. In addition, when it is required to change the scanning path after generation of the scanning path information, it was necessary to again obtain the shape data.
Moreover, the automatic ultrasonic flaw inspection method disclosed in Patent Document 2 can prepare shape data with distance data at a small number of points by performing the interpolation using the spline function. However, in order to generate the scanning path information with higher accuracy, it is essential to obtain distance data at a larger number of points so as to eliminate a need for an interpolation as much as possible.